Among the fluorine-containing propenes represented by the chemical formula CF3CF═CX1X2, wherein X1 is a hydrogen atom or a chlorine atom, and X2 is a fluorine atom, a chlorine atom or a hydrogen atom, 2,3,3,3-tetrafluoropropene represented by CF3CF═CH2 (HFC-1234yf) is a compound usable as a refrigerant. The fluorine-containing propene represented by the chemical formula CF3CF═CClX, wherein X is a chlorine atom, a fluorine atom or a hydrogen atom, is an intermediate that is useful for producing various kinds of fluorocarbons.
One example of the heretofore known methods of preparing the fluorine-containing propene represented by the chemical formula CF3CF═CX1X2 is directly fluorinating the carbon at the allylic position of propene that has at least one halogen atom bonded to a double bonded carbon atom (see Non-Patent Literature (NPL) 1 and NPL 2 below). However, because SbF3 is used as a fluorinating agent in this method, more than one equivalent weight of SbF3, based on fluorine atoms, per an equivalent weight of the starting propene, is necessary. This makes the process uneconomical and incurs additional cost for the waste treatment. Furthermore, because the reaction is conducted in a liquid phase, its handling is difficult. Moreover, in the case where two or more chlorine atoms are bonded to the allylic position, when all of these chlorine atoms are substituted with fluorine atoms, decomposition may follow and the yield remarkably decreases to as low as 60% or less, requiring improvement in the yield. Further, the reaction in this method should be conducted under the application of pressure and heating, making the treatment process complicated.
Regarding the compound represented by CF2ClCF═CFCl (CFC-1214yb), there is a report that not the chlorine at the allylic position of propene but the chlorine bonded to the double bonded carbon atom is preferentially replaced with fluorine by the fluorination reaction, so that CF2ClCF═CF2 (CFC-1215yc) is formed (see Patent Literature (PTL) 1 below).
Currently, there are many reports regarding the processes for preparing a fluorine-containing propene represented by CF3CF═CClX, wherein X is Cl, H or F. Specific examples of such processes include, other than the process conducting fluorination using SbF3 described above, a process wherein fluorine-containing propane is subjected to dehydrohalogenation, a process wherein fluorine-containing propane is subjected to dehalogenation (i.e., removing FCl or Cl2), a process wherein a halogen in fluorine-containing propene is dislocated to form a desired object, etc. Various methods for producing CF3CF═CCl2 (CFC-1214ya) are reported, for example, subjecting CF3CF2CHCl2 (HCFC-225ca) to dehydrofluorination (see PTL 2, PTL 3, etc.), subjecting CF3CFClCCl3 (CFC-214bc) to dechlorination (see NPL 3), exchanging chlorine with fluorine in CF3CCl═CCl2 (CFC-1213xa), CF3CCl═CFCl (CFC-1214xb), CF3CF═CFCl (CFC-1215yb) or like starting material using a chromium oxide in the presence of hexafluoropropylene (NPL 4), etc. However, in these methods, the halogen elimination is conducted after forming propane, the number of steps increases and the utilization efficiency of halogen becomes undesirably low. None of these methods achieve a satisfactory yield. In particular, in the method comprising the step of dislocating halogen, the reaction system becomes complicated because many components are involved in the reaction, resulting in very low yield.